Heredity Project

Health Problems Caused by a Single Gene

For comparison, here is what the smiley/frown model looks like for health problems that are caused by a single gene (either autosomal dominant or autosomal recessive). In the images below, larger faces represent a gene that causes a genetic disease. Smaller faces are included to make the point that other genetic, environmental, and lifestyle factors play a role in overall health status, even when one gene is sufficient to cause a particular genetic disease. To learn more about autosomal dominant and autosomal recessive inheritance, refer to the resources on our Links page.

Faulty forms of the genes described here are relatively rare compared to the risk genes described elsewhere on this site. Since the faulty forms are rare, most people have two normal gene copies.

Autosomal Dominant

Health problems where one faulty copy of the relevant gene is enough to cause a genetic disease

Most people have two normal gene copies and are healthy. Having one copy of the faulty gene is enough to cause the disease. Examples are hereditary breast cancer, Huntington disease, polycystic kidney disease, and other autosomal dominant diseases.

Autosomal Recessive

Health problems where both copies of the relevant genes must be faulty for a person to have that particular disease

Typically, both parents of an affected person have one faulty copy and one normal copy. Children are affected when, by chance, they receive two faulty copies. Examples are cystic fibrosis, sickle cell anemia, hereditary hemochromatosis, and other autosomal recessive diseases.

To learn more about any of the health problems mentioned here, refer to the "Resources for Specific Conditions" on our Links page.